Alba form of orchids
 

Hi guys, I’ve been thinking about how alba form orchids occur because my friend has a dimorphorchis lowii which turned out to be alba and that got me thinking for example are there statistics on the chance of one being alba and what causes an orchid to be alba

JonathanX - Welcome to the Orchid Board!

Your friend has a very distinctive plant that is probably worth a lot of money. He should divide it when it's big enough and get it into the hands of a commercial grower who can propagate it.

Albas occur when a mutation on all pertinent chromosomes renders inactive one or more enzymes necessary for producing pigment. If two albas with different nonfunctional enzymes are crossed, resultant seedlings may be all normal, because each parent contributes one normal copy of the defective enzyme from the other parent. But those seedlings may carry and pass on the mutations.

Interesting question.

We were just having a discussion about that very topic regarding people seeing alba form Cypripedium acaule (pink lady slipper) this year. I came across a bed of close to 100 plants and fully 1/3 were white. Have never seen so many. It's usually 1 or 2 and not very common at all.

ES has it right, but there is more to the story.

In Paphs:

• Brachys are not true albas, but they suppress pigment production when bred with other Paphs.
• Alba forms of niveum & bellatulum are not compatible. If bred, offspring is 100% colored. This means that the 'albinism' lies on different genes in these two species.

Also, all white orchids are not albas. For example, V. (formerly Neofinetia) falcata has a white flower, but it is not an alba. I purchased a hybrid bred from Neo. falcata & Asctm. ampullaceum album. When it finally bloomed, it was standard ampullaceum pink (since the white falcata is not an alba, it overrode the album genes from the ampullaceum side).

In Cattleya walkeriana , a Brazilian orchid which is highly studied and bred here, there are 4 genes located in different chromosome pairs which determine the orchid's color form. The gene C determines the production of chromogens, and the gene R determines the production of enzymes which turn the chromogens into pigment. The Dominant form Cc, or CC means there will be chromogen, whereas the recessive form cc means there will be no chromogens produced and the plant will be semi-alba, alba, or coerulea, but not "tipo", which is the regular pink form. If there is chromogen and the plant does not produce the converting enzyme then the same will happen, the plant will not be pink. This is the case for plants with the gene combination rr. In the case of Rr or RR the plant will produce the enzyme.
Then there are other genes such as P, which determines if the plant will be alba (the dominant form Pp or PP) or semi-alba (the recessive form pp). And there is the gene C which determines if the plant will have the coerulea form (the recessive cc) or not (Cc or CC).

So in practice, what does this say about orchid colors when it comes to reproduction and crossing two plants together? Well, two alba plants may result in a pink plant: For example, lets say plant A gas the genotype CcrrPpCc, and plant B has the genotype ccRrPpCc. Then one of the plants resulting from the crossing may have the genotype CcRrppcc, and in this case the plant will be pink. The only way to assure all resulting plants will be alba is if the two parents are double recessive ( have the genotype ccrr ... ). So a plant can have the fenotype of an alba, but carry the genes to produce a pink plant. And a pink plant can also carry the genes to produce an alba.